One method of suppressing noise in jet engines is to baffle the intake with an acoustical panel. In the Boeing 737-300 series aircraft, such panels comprise a trilaminate of a perforated aluminum alloy sheet, a honeycomb aluminum alloy core and a solid aluminum alloy backing sheet. This laminate is located in the engine cowel such that a portion of the intake air flows through the holes in the perforate sheet and reverberates in the honeycombs, thereby damping undesired frequencies and harmonics. The three layers of the laminate are held together by a cured epoxy adhesive. However, if epoxy adhesive blocks the holes in the perforate top sheet, noise suppression characteristics may be inhibited. It is also desirable to form a uniform adhesive bond between layers to optimize noise reduction performance.
In a past laminate fabrication method, a sheet of tacky epoxy resin was applied to one side of the aluminum honeycomb core. To prevent the epoxy from blocking air flow, the resin was heated with a quartz lamp and the honeycomb core was manually passed over an air knife, clearing epoxy away from the cell openings. As the epoxy cleared from the honeycomb openings, it collected on the cell edges and walls. The adhesive coated honeycomb was later mated to a clean perforated aluminum sheet by heating in an autoclave.
This method is described in U.S. Pat. No. 4,249,974 assigned to the assignee hereof and incorporated herein by reference. Related U.S. Pat. No. 4,155,800 claims reticulated honeycomb product made by the method of the '974 patent.
This process was difficult to control in both the heating and honeycomb-clearing stages. If too much heat was applied the epoxy would cure prematurely and if too little was applied the epoxy was prone to blow off the core altogether. Similarly, if the air knife was brought too close, it could blow the adhesive off completely or if it was held too far away, the honeycombs would not clear. Accordingly, it was often necessary to patch an adhesive coated honeycomb by hand before making a lamination. Moreover, considerable epoxy splitter was generated.
According, I have developed a novel method and an apparatus for clearing adhesive from the holes of a perforated substrate and creating a uniform layer of curable adhesive thereon. This process may be referred to herein as reticulation or reticulating.